This invention relates generally to towed vehicle brake controllers and, in particular, to a novel towed vehicle brake controller which can be retrofitted to a towing vehicle to effect a gradual application of the towed vehicle brakes proportional to the movement of the towing vehicle brake pedal.
Towed vehicles, such as recreational and utility trailers adapted to be towed by automobiles and small trucks, are commonly provided with electric brakes. The electric brakes generally include a pair of brake shoes located at each wheel which, when actuated, frictionally engage a brake drum on the towed vehicle. An electromagnet is mounted on one end of a lever to actuate the brake shoes, and is drawn against the rotating brake drum when an electrical current is applied, thereby pivoting a lever to actuate the brake shoes. Typically, the braking force provided is proportional to the electrical current applied to the electromagnet. The electrical current may run as high as 12 amperes on a double axle trailer.
Early trailer brake controllers for towed vehicles tied directly into the towing vehicles' braking system, either by tapping into the brake lines of the towing vehicle to determine the brake pressure or determining the position of the brake pedal with different types of linkages to determine the pedal position and to then apply the brakes of the towed vehicle accordingly. Some controls used a timer tied to the towing vehicle's brake lights that would gradually apply trailer brakes over a period of seconds.
Current commercially available controllers (apart from some integrated vehicle controllers) generally are either timer based controllers or velocity sensor based controllers.
In timer based controllers, the towed vehicle brakes are engaged a set time period after the towing vehicle brakes are engaged. The time period is set by the driver and is often adjustable. These controllers are typically tied into the brake light system, to be activated when the brake lights are activated. In timer based control systems, braking increases at a preset rate until the brakes are released or maximum braking is reached. Such systems are of simple design, are inexpensive, and are easy to mount. However, because they are time based, the braking of the towed vehicle is not proportional to the braking of the towing vehicle. Further, they must be connected to the brake indicator system.
In a velocity sensor based controller, the towed vehicle's brakes are applied in a proportional manner according to changes in velocity of the towing vehicle. Velocity changes are sensed either by pendulum based sensors or accelerometer chips. True velocities are not detected, only changes in “g-forces” are detected. Unlike the timer based systems, velocity sensor based systems provide for a form of proportional braking when deceleration is detected. These velocity sensor based systems are responsive to changes in speed, rather than braking activity, and can thus be fooled by road conditions and/or vehicle orientation. Also, like the timer based systems, the velocity sensor based systems require connectivity to the towing vehicle's brake indicator system.
Current towed vehicle brake controllers suffer from the flaw that they try to infer braking activity, rather than measuring braking activity. Therefore, typical timer-based systems or velocity sensor based systems apply the brakes of the towed vehicle after the brakes have been applied to the towing vehicle. However, it is preferable to begin application of the towed vehicle brakes prior to application of the towing vehicle brakes so that the towed vehicle will begin slowing down prior to, and no later than, the time the towing vehicle begins to slow down. This issue was solved by the controller described in my U.S. Pat. No. 6,050,649, which is incorporated herein by reference. The controller of that patent has worked well. However, it can be improved.